This project addresses the regulation of neuropeptide expression in chronic pain that appears following spinal cord injury. Such pain is often a severe affliction for the victim. A model established in our laboratories to investigate the pain that follows spinal cord injury will be utilized. In this model, pain-like behaviors that appear following hemisection of the rt spinal cord are assessed. The model reproduces the salient features of post spinal cord injury in humans. Our central hypothesis is that expression of the cytokine leukemia inhibitor factor (LIF) counteracts the development of chronic pain following spinal cord injury by increasing the expression of the neuropeptide galanin and decreasing the expression of the peptides nerve growth factor (NGF), substance and calcitonin gene related peptide. This hypothesis includes a sub-hypothesis that LIF acts on the synthesis of the latter peptides by reducing the biosynthesis of NGF. Existing evidence suggests that increased LIF reduces manifestations of pain in peripheral neuropathy and inflammation models by altering the production of neuropeptide inter cellular messengers. However, since this is unaddressed for the pain that develops following spinal cord injury, the biosynthesis of all of the above peptides and their effects on pain-like behaviors following spinal cord injury will be characterized. Time courses of effects of injury on peptide biosynthesis will be determined by analyzing peptides in tissue from the area of injury by ELISA or RIA assays and by immunocytochemistry. Roles of these peptides in pain expression will be tested by blocking their actions during times of increased expression or adding them when their expression is decreased, together with measuring pain-like behaviors in the experimental animals. The actions of LIF or NGF will be manipulated so as to increase peptide synthesis and then the action of that peptide will be blocked to establish whether modulation of peptide biosynthesis by LIF and NGF influences pain-like behaviors. Effects of LIF of inflammation and associated pain will also be characterized. Insights from this work will aid in developing treatments for pain that appears following spinal cord injury, currently a clinically intractable problem.